The instant invention relates to protection thyristors and triacs.
A protection thyristor or triac is a component with two main electrodes that can be located between two terminals of a circuit to be protected, for example, between the terminals of a telephone set, between the current supply terminals of a circuit, etc. The protection thyristor is normally non-conductive but becomes conductive when it receives through its terminals a reverse-polarity voltage overcoming a well-determined threshold that is called break-over voltage. Under direct polarity voltages, the thyristor is blocked.
The protection triac is non-conductive for both polarities but becomes conductive over a certain threshold (break-over voltage) for the direct polarity as well as for the reverse polarity.
In the hereinunder description, the protection thyristors only will be mentioned, the invention being also applicable to a triac constituted of two reverse-connected thyristors.
The protection thyristors are distinguished from the conventional switching thyristors not only by their inner structure, in which the diffusion profiles of the various regions are chosen for carrying out the automatic triggering function that is assigned to them (triggering for as accurate a voltage as possible, but also by the fact they do not have gate electrodes.